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Background: Focal electrically administered therapy is a new method of transcranial electrical stimulation capable of focal modulation of cerebral activity. Other than invasive studies in animals and examination of motor output in humans, there are limited possibilities for establishing basic principles about how variation in stimulus parameters impact on patterns of intracortical stimulation. This study used a simpler paradigm and evaluated the effects of different stimulation parameters on subjective perception of the quality and location of scalp pain.

Methods: In 2 studies, 19 subjects were randomly stimulated over the left forehead, varying the anode-cathode arrangement, the intensity of stimulation, the electrode size and placement, and whether the current flow was unidirectional or bidirectional. Subjects rated the location of the sensation and its quality.

Results: The perceived center of stimulation moved toward the cathode, regardless of placement. This shift in subjective sensation was more prominent when the electricity was unidirectional. In addition, more intense stimulation, as well as stimulation with a smaller electrode, caused greater perceived pain. Unidirectional stimulation was rated more painful when traveling from a large anode to a small cathode and less painful when traveling from a small anode to a large cathode. Finally, participants were more likely to perceive the electrical stimulation as moving toward a specific direction when the intensity was high than when it was low.

Conclusions: The intensity and location of sensations can be manipulated by varying the intensity, current direction, or geometry of electrodes.

From the *Psychiatry Department, Brain Stimulation Laboratory, Medical University of South Carolina, Charleston, SC; †Departments of Physiology and Neurology, State University of New York, Brooklyn; ‡James Long Company; and §Columbia University, New York, NY.

The Brain Stimulation Laboratory is supported in part by the Stanley Foundation, the National Alliance for Research on Schizophrenia and Depression, National Institute of Neurological Disorders and Stroke grant RO1-AG40956, National Institute of Mental Health grant RO1 MH069887, 1K08MH070915-01A1 (Z.N.), and 1K23NS050485-01A2 (J.J.B.).